The following description provides a summary of information relevant to the present disclosure and is not a concession that any of the information provided or publications referenced herein is prior art to the claimed invention.
The SELEX process is a method for the in vitro selection of nucleic acid molecules that are able to bind with high specificity to target molecules and is described in U.S. Pat. No. 5,475,096 entitled “Nucleic Acid Ligands” and U.S. Pat. No. 5,270,163 (see also WO 91/19813) entitled “Nucleic Acid Ligands” each of which is specifically incorporated by reference herein. These patents, collectively referred to herein as the SELEX Patents, describe methods for making an aptamer to any desired target molecule.
The basic SELEX process has been modified to achieve a number of specific objectives. For example, U.S. Pat. No. 5,707,796, entitled “Method for Selecting Nucleic Acids on the Basis of Structure” describes the use of the SELEX process in conjunction with gel electrophoresis to select nucleic acid molecules with specific structural characteristics, such as bent DNA. U.S. Pat. No. 5,580,737, entitled “High-Affinity Nucleic Acid Ligands That Discriminate Between Theophylline and Caffeine” describes a method for identifying highly specific aptamers able to discriminate between closely related molecules, termed Counter-SELEX. U.S. Pat. No. 5,567,588, entitled “Systematic Evolution of Ligands by Exponential Enrichment: Solution SELEX” describes a SELEX-based method which achieves highly efficient partitioning between oligonucleotides having high and low affinity for a target molecule. U.S. Pat. No. 5,496,938, entitled “Nucleic Acid Ligands to HIV-RT and HIV-1 Rev” describes methods for obtaining improved aptamers after SELEX has been performed. U.S. Pat. No. 5,705,337, entitled “Systematic Evolution of Ligands by Exponential Enrichment: Chemi-SELEX” describes methods for covalently linking an aptamer to its target.
The SELEX process encompasses the identification of high-affinity aptamers containing modified nucleotides conferring improved characteristics on the ligand, such as improved in vivo stability or improved delivery characteristics. Examples of such modifications include chemical substitutions at the ribose and/or phosphate and/or base positions. SELEX process-identified aptamers containing modified nucleotides are described in U.S. Pat. No. 5,660,985, entitled “High Affinity Nucleic Acid Ligands Containing Modified Nucleotides” that describes oligonucleotides containing nucleotide derivatives chemically modified at the 5′- and 2′-positions of pyrimidines. U.S. Pat. No. 5,580,737, see supra, describes highly specific aptamers containing one or more nucleotides modified with 2′-amino (2′-NH2), 2′-fluoro (2′-F), and/or 2′-O-methyl (2′-OMe).
Further modifications of the SELEX process are described in U.S. Pat. No. 5,763,177, U.S. Pat. No. 6,001,577, and U.S. Pat. No. 6,291,184, each of which is entitled “Systematic Evolution of Nucleic Acid Ligands by Exponential Enrichment: Photoselection of Nucleic Acid Ligands and Solution SELEX”; see also, e.g., U.S. Pat. No. 6,458,539, entitled “Photoselection of Nucleic Acid Ligands”. These patents, collectively referred to herein as “the PhotoSELEX Patents” describe various SELEX methods for selecting aptamers containing photoreactive functional groups capable of binding and/or photocrosslinking to and/or photoinactivating a target molecule. The resulting photoreactive aptamers are referred to as photocrosslinking aptamers or photoaptamers.
Although these SELEX and photoSELEX processes are useful, there is always a need for processes that lead to improved properties of aptamers generated from in vitro selection techniques. For example, a need exists for aptamers to target molecules with better binding affinities than those achieved with naturally occurring DNA or RNA nucleotides, as well as methods for producing such aptamers. For many applications, such as for example, in vitro assays, diagnostics, therapeutic, or imaging applications, it is of interest to produce aptamers with slow dissociation rates from the aptamer/target affinity complex. Several techniques have been proposed for producing such reagents (see, e.g., WO 99/27133 and US 2005/0003362). However, these selection processes do not discriminate between the selection of reagents that have fast association kinetics with the target (i.e., fast on-rates) and the selection of reagents that have slow dissociation kinetics with the target (i.e., slow off-rates). Thus, there is a need for novel processes and techniques that favor the selection of slow off-rate aptamers while inhibiting the selection of aptamers that simply have a fast association rate with the target.
Finally, there is a need for aptamer constructs that include different built-in functionalities. These functionalities may include tags for immobilization, labels for detection, means to promote or control separation, etc.